U.S. patent number 8,319,499 [Application Number 12/668,415] was granted by the patent office on 2012-11-27 for coated motor vehicle battery sensor element and method for producing a motor vehicle battery sensor element.
This patent grant is currently assigned to Auto Kabel Managementgesellschaft mbH. Invention is credited to Frank Gronwald, Franz-Josef Lietz.
United States Patent |
8,319,499 |
Gronwald , et al. |
November 27, 2012 |
Coated motor vehicle battery sensor element and method for
producing a motor vehicle battery sensor element
Abstract
The invention relates to a motor vehicle battery sensor element
comprising a resistor element 2 and at least two spatially
separated electric contacts 16 positioned on the resistor element
2. To increase the measuring accuracy and to reduce the temperature
variance, it is proposed that the resistor element 2 along with the
electric contacts 16 is coated with a metal coating 8.
Inventors: |
Gronwald; Frank (Bedburg,
DE), Lietz; Franz-Josef (Oberhausen-Lirich,
DE) |
Assignee: |
Auto Kabel Managementgesellschaft
mbH (Hausen i.W., DE)
|
Family
ID: |
39118771 |
Appl.
No.: |
12/668,415 |
Filed: |
January 18, 2008 |
PCT
Filed: |
January 18, 2008 |
PCT No.: |
PCT/EP2008/050572 |
371(c)(1),(2),(4) Date: |
February 05, 2010 |
PCT
Pub. No.: |
WO2009/010313 |
PCT
Pub. Date: |
January 22, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100201369 A1 |
Aug 12, 2010 |
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Foreign Application Priority Data
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Jul 13, 2007 [DE] |
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10 2007 033 182 |
Sep 24, 2007 [WO] |
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PCT/EP2007/060104 |
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Current U.S.
Class: |
324/430; 73/776;
361/91.2; 361/26 |
Current CPC
Class: |
G01R
31/364 (20190101); H01C 1/144 (20130101); H01C
1/14 (20130101); G01R 1/203 (20130101); G01R
31/3644 (20130101) |
Current International
Class: |
G01N
27/416 (20060101); G01L 1/00 (20060101); H02H
5/04 (20060101); H02H 3/20 (20060101) |
Field of
Search: |
;324/430
;361/26,34,88,91.2,93.8,103,163 ;73/776 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1808147 |
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Jul 2006 |
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CN |
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102004040575 |
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Aug 2004 |
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DE |
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102004007851 |
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Sep 2005 |
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DE |
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102004049153 |
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Apr 2006 |
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DE |
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102005019569 |
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Nov 2006 |
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DE |
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0193854 |
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Feb 1986 |
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EP |
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1028436 |
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Aug 2000 |
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EP |
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1030185 |
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Aug 2000 |
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EP |
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0990167 |
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Jun 2006 |
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EP |
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Other References
European Patent Office, International Search Report,
PCT/EP2008/05072, May 9, 2008. cited by other .
Braudaway, David W., Precisiion Resistors: A Review of Material
Characteristics, Resistor Design and Construction Practices, IEEE
Transactions on Instrumentation and Measurement, vol. 48, Nr:5,
ISSN 0018-9456. cited by other .
The State Intellectual Property Office of the People's Republic of
China, Office Action, Application No. 200880024424.4, dated Feb.
13, 2012, 7 pages. cited by other.
|
Primary Examiner: Diao; M'Baye
Attorney, Agent or Firm: Sunstein Kann Murphy & Timbers
LLP
Claims
The invention claimed is:
1. A motor vehicle battery sensor element comprising: a resistor
element; and at least two spatially separated electrical contacts
positioned on the resistor element, wherein the resistor element
along with the electrical contacts is coated with a metal coating,
such that the thermoelectric potential between the electrical
contacts and the resistor element is short-circuited via the
coating.
2. The motor vehicle battery sensor element of claim 1, wherein the
coating is a tin coating.
3. The motor vehicle battery sensor element of claim 1, wherein the
thermoelectric potential between the electrical contacts and the
resistor element is between 0.1 .mu.V/K and 1 .mu.V/K.
4. The motor vehicle battery sensor element of claim 1, wherein the
coating has a thickness of between 1 .mu.m and 10 .mu.m.
5. The motor vehicle battery sensor element according to claim 1,
wherein the resistor element in the temperature range from
20.degree. C. to 50.degree. C. has a temperature coefficient in the
range 10.sup.-6 to 10.
6. The motor vehicle battery sensor element of claim 1, wherein the
resistor element has a temperature coefficient compensating for the
temperature coefficient of the coating such that the effect of the
temperature coefficient on the overall resistance is essentially
compensated.
7. The motor vehicle battery sensor element according to claim 1,
wherein the electrical contacts are made from a non-ferrous metal,
in particular copper.
8. The motor vehicle battery sensor element of claim 1, wherein the
resistor element is made from two flat parts connected with each
other together by a material closure.
9. The motor vehicle battery sensor element of claim 1, wherein a
first flat part is a resistance piece in the form of a measuring
resistor and a second flat part is a connection piece made from a
non-ferrous metal.
10. The motor vehicle battery sensor element of claim 1, wherein
the resistor element is at least in part made from one or more of
NiCu30Fe, CuMn12Ni, Cu,Ni30Mn, NiFe30, CuNi23Mn, CuMn7Sn, CuNi15,
CuNi10, CuMn3, CuNi6, Ni99.6, Ni99.4Fe1 Ni99.98, CuNi2, CuNi1,
E-Cu57 and W.
11. The motor vehicle battery sensor element of claim 1, wherein
the resistor element is connected with a battery pole clip by a
material closure.
12. The motor vehicle battery sensor element of claim 1, wherein
the resistor element is connected with a power conductor leading to
consumers by a material closure.
13. The motor vehicle battery sensor element of claim 1, wherein
the electrical contacts are in the form of flat or round conductors
positioned flat on the surface of the resistor element.
14. The motor vehicle battery sensor element of claim 1, wherein
the electrical contacts are positioned essentially orthogonally to
the direction of the current in the resistor element on the surface
of the resistor element.
15. The motor vehicle battery sensor element of claim 1, wherein
the ends of the electrical contacts are formed to accommodate an
integrated circuit which assesses at least the electrical voltage
between the contacts.
16. The motor vehicle battery sensor element of claim 1, wherein
the electrical contacts are soldered to the integrated circuit.
17. The motor vehicle battery sensor element of claim 1, wherein
the electrical contacts have a spatial distance of 1 mm-50 mm,
preferably 5 mm-10 mm.
18. The motor vehicle battery sensor element of claim 1, wherein
the electrical contacts are positioned on at least one of A) in the
area of the resistance piece, B) the transitions between the
resistance piece and the connection pieces, and C) the connection
pieces.
19. A method for producing a motor vehicle battery sensor element
comprising: arranging of two spatially separated electrical
contacts on a resistor element, electrically connecting of the
contacts with the resistor element; and metal coating of the
contacts together with the resistor element, such that the
thermoelectric potential between the electrical contacts and the
resistor element is short-circuited via the coating.
20. The method of claim 19, further comprising tinning of the
electrical contacts together with the resistor element.
21. The method of claim 19, further comprising metal coating of the
electrical contacts together with the resistor element by at least
one of immersion, galvanization, and powder coating.
Description
The application relates to a motor vehicle battery sensor element
with a resistor element and at least two spatially separated
contacts positioned on the resistor element. The invention also
relates to a method for producing such a motor vehicle battery
sensor element.
Present-day motor vehicles have an ever-increasing number of
electrical consumers. Apart from the essential engine functions
which are electrically powered, such as for example the starter
motor, motor vehicles contain a large number of comfort consumers,
such as for example air conditioning, navigation system, onboard
computer, maintenance electronics and so on. The large number of
comfort consumers leads to an increased load on the motor vehicle
battery. Even when the motor vehicle is at a standstill, power is
being demanded from the battery. This means that the battery is no
longer used just for the original tasks of powering the starter
motor with starter current, but provides all the electronics in the
motor vehicle with energy. Due to the discharging of the battery
when the vehicle is at a standstill, it may be that there is
insufficient starter current available for starting. This is
something that must be avoided.
For the above reasons it is necessary to be able to reliably
determine the state of the battery. To this end in the past a
variety of motor vehicle battery sensors have been proposed. These
motor vehicle battery sensors are preferably positioned directly on
the battery terminals.
Thus, for example, from EP 0 990 167 a battery terminal is known,
which via a resistor (shunt), apart from the current in the power
conductors of the battery, also measures the voltage and/or
temperature and for example using these values assesses the state
of the battery. In order to assess the state of the battery it is
necessary to be able to precisely measure the voltage dropping via
the shunt. The assessment is highly dependent upon the quality of
the voltage tap via the shunt. Thus an accurate measurement is
determined by how the voltage taps and the measurement electronics
are positioned on the shunt.
With the resistor elements known today it is necessary to position
a resistance piece between two connection pieces. So these days,
for example, a CuMn12Ni-alloy (Manganin) is used as the resistance
piece. The Manganin is positioned between two connection pieces in
non-ferrous metal, for example copper. During production the
connection pieces, which for example have a flat design, are welded
to the resistance piece with a flat design by means of electron
beam welding. Here the flat part in Manganin can be thinner than
the flat parts of the connection pieces, so that the resistance
piece forms an indentation in the surface of the resistor element.
On the cooper connection pieces are positioned connection supports,
which are likewise in copper. An integrated circuit is soldered to
the connection supports, with which at least the physical measures
of current, voltage and/or temperature of the resistance piece can
be evaluated.
It has been discovered, however, that thermoelectric potential
results in the transition from copper to Manganin. This
thermoelectric potential leads to interference with the measurement
results of the measurement electronics. The Seebeck effect is for
example responsible for the thermoelectric potential. Therefrom, a
current results within a conductor if there is a heat flow. In the
event that the connection supports are positioned directly on the
Manganin, a thermoelectric potential results which influences the
measurement result in a temperature variant manner. The
thermoelectric potential is also known as the thermoelectric force
and is caused by a temperature-dependent flow of electrons. The
thermoelectric potential can be determined by:
U=(K.sub.a-K.sub.b)(T.sub.1-T.sub.2) where U: voltage, K: K-value
of the material, T1; T.sub.2: temperature of the materials at the
point of connection. Copper has a K-value of 0.7 mV/100K.
The disadvantages outlined above pose the problem of providing a
resistor element for a motor vehicle battery sensor which is
essentially temperature invariant.
The problem derived and demonstrated above from the prior art is
solved in that the resistor element, along with the electrical
contacts, is coated with a metal coating.
It has been discovered that by a seamless metal coating of the
resistor element together with the electrical contacts the effect
of the thermoelectric potential between the resistor element and
the electrical contacts on the measurement result can be reduced,
preferably eliminated.
If a thermoelectric potential does arise between the contacts and
the resistor element, this can be short-circuited by the coating.
The electrical contacts can for example, be positioned directly on
the shunt, resulting in a temperature-dependent thermoelectric
potential between the shunt and the contacts. To compensate for
this contact voltage the metal coating is provided. The metal
coating is able to electrically short-circuit the thermoelectric
potential and thus compensate for its effect on the measurement
result. The electrical tapping of the sensor takes place via the
contacts. At the electrical tap the thermoelectric potential
between the resistor and the electrical contacts is essentially
compensated.
The metal coating represents in the electrical equivalent circuit
diagram a resistor positioned in parallel to the measurement
electronics, which resistor lies parallel to the measuring resistor
element. The effect of the resistance of the metal coating is, for
example, in the range between 1 and 3% of the total resistance of
the measuring resistor.
It has become apparent that a coating in tin (SN) has the necessary
characteristics. Through the metal coating the surface protection
of the contacts and of the resistor element is also achieved. It is
known that electrical contacts can oxidise and thus when tapping
via the electrical contacts an increased contact resistance
results. By using a tin coating oxidation of the electrical
contacts can be lessened.
The thermoelectric potential between the electrical contacts and
the resistor element or between the connection pieces and
resistance piece of the resistor elements can be between 0.1
.mu.V/K and 10 .mu.V/K, preferably between 0.4 .mu.V/K and 0.8
.mu.V/k. This is the case, for example, when Manganin is used as
the resistance piece of the resistor element and copper as the
electrical contact or connection piece.
A layer thickness of the coating of between 1 .mu.m and 10 .mu.m,
preferably of between 5 .mu.m and 8 .mu.m, is preferred. For a
distance between the electrical contacts of approximately 10 mm,
such a coating leads to a resistance of the coating between the
electrical contacts of approximately 8,000 .mu..OMEGA.. Where the
resistance of the resistance piece, for example of the shunt, is
110 .mu..OMEGA., from the parallel connection of these two
resistances a total resistance of 108.6 .mu..OMEGA. results.
In order to be able to reduce the effects of temperature on the
measurement result, it is proposed that the temperature-dependent
resistance of the coating is essentially compensated by the
temperature-dependent resistance of the resistor element. Where tin
is used, for example, the temperature-dependent change in the
resistance (temperature coefficient) of the coating can distort the
measurement result. With a precision measuring shunt, however, this
is a disadvantage. Therefore through a suitable choice of resistor
element the temperature-dependent change in the resistance of the
coating can be counteracted. For example, the resistor element can
be selected so that the total resistance from the connection in
parallel between the coating and the resistor element is
essentially temperature-independent.
For example, the temperature coefficient .alpha..sub.20 of the
coating can be in the range 110.sup.-3 to 910.sup.-3 1/K,
preferably 6.10.sup.-3 1/K. The temperature coefficient
.alpha..sub.20 of the resistor element can for example be the
inverse of this. The temperature coefficient .alpha..sub.20 of the
resistor element can also be 1010.sup.-6 1/K.
The electrical contacts can be positioned directly on a resistance
piece, for example made from Manganin, of the resistor element. In
the event of temperature changes the resistances vary as a function
of the temperature coefficients according to:
R(T)=R(T.sub.0)(1+.alpha..sub.T0(T-T.sub.0)) where R: resistance,
T: temperature, T.sub.0: starting temperature, preferably
20.degree. C., .alpha..sub..tau.o: temperature coefficient at
starting temperature.
According to an advantageous exemplary embodiment the electrical
contacts are made from a non-ferrous metal, for example copper. The
copper contacts allow good contacting with measurement electronics
for measurement of the battery current and/or the temperature.
According to an advantageous exemplary embodiment the resistor
element can be made from two flat parts firmly bonded together. For
example, a resistance piece can be formed from Manganin and a
connection piece from copper.
According to an advantageous embodiment the first flat part is a
resistance piece in the form of a measuring resistor and a second
flat part is a connection piece made from non-ferrous metal.
By placing the contacts flat on the surface of the resistor element
the contacts serve directly as spacers for an integrated circuit,
so that contact between integrated circuit and resistor element
beyond the contacts can be avoided. Because the resistor element is
designed as a flat part, the contacts can be positioned flat along
the resistor element.
Preference is for the use of the materials NiCu30Fe, CuMn12Ni,
CuNi30Mn, NiFe30, CuNi23Mn, CuMn7Sn, CuNi15, CuNi10, CuMn3, CuNi6,
Ni99.6, Ni99.4Fe, Ni99.98, CuN12, CuNi1, E-Cu57 or W. These alloys
or materials are particularly well-suited as the resistor element,
since they allow a precise determination of the voltage and of the
current.
In order to be able to directly measure the temperature of the
battery, it is proposed that the resistor element is connected with
a battery pole clip by material closure. In this case the battery
pole clip can be directly connected to a battery pole and the
temperature of the battery pole is transmitted to the resistor
element.
In order to be able to supply the electrical consumers of the motor
vehicle with the battery current, it is proposed that the resistor
element is firmly bonded with a power conductor leading to the
consumer.
According to an advantageous embodiment it is proposed that the
contacts are in the form of flat or round electrical conductors
positioned flat on the surface of the resistor element. For
example, it is possible to position a round wire along the surface
of the flat part and connect this electrically to the resistor
element. If the contacts are located at a defined distance from one
another, then it is possible via the voltage measured between the
contacts to determine the current flow in the resistor element.
Through a large contact area between the contacts and the resistor
element it is possible to guarantee a precise temperature sensing
in an integrated circuit connected to the contacts. It is also
possible for flat profiles acting as conductors to be brought into
contact with the resistor element in order to form the
contacts.
It is also proposed that the contacts are positioned essentially
orthogonally to the direction of the current in the resistor
element on the surface of the resistor element. The flat
positioning of the contacts on the resistor element can essentially
take place along a line. A flat positioning of the contacts on the
resistor element, unlike a point by point positioning, apart from a
low contact resistance and good thermal conductivity, also provides
a support function for an integrated circuit positioned on the
contacts.
In order to create a good electrical contact between resistor
element and contact, it is proposed that the contacts are connected
with the resistor element by material closure (firmly bonded,
material locking, material fit).
Such a material closure can be created, for example, by means of
ultrasonic welding. Ultrasonic welding avoids spattering of
material on the resistor element and thereby possibly distorting
the measurement results. Good electrical contacting and high
mechanical load-bearing capacity of the contacts for an integrated
circuit are achieved by the contacts essentially being connected
flat with the resistor element along their direction of
extension.
It is not necessary for the contacts laying flat on the flat part
to be contacted with the resistor element along the entire contact
surface. It is also possible for the contacts to be connected with
the resistor elements only intermittently by material closure.
The largest possible contact area between contacts and resistor
elements is guaranteed by the contacts being positioned on the
broad surface of the resistor element in the form of a flat
part.
A particularly easy contacting of an integrated circuit with the
contacts is guaranteed by the contacts being bent at both ends so
that contact pins protrude essentially orthogonally from the
surface plane of the resistor element. For example, it is possible,
during manufacture, to allow the contacts to protrude beyond the
edges of the resistor element. In this way it is possible, for
example, to extend the contacts, which may for example be in the
form of wires, so that their length is slightly greater than the
width of the resistor element. After material bonding with the
resistor element the ends of the wires stick out beyond the edges
of the resistor. In a further production stage the resistor element
connected to the contacts can for example be pushed into a mould
which presses out the parts of the contacts extending beyond the
edges from the plane of the surface of the resistor element. The
contact pins formed in this way protrude from the plane of the
resistor element and are particularly well-suited for electrical
contacting with an integrated circuit.
The contacts serve for contacting with an integrated circuit, so
that with the help of the integrated circuit at least the
electrical voltage between the contacts can be assessed.
Through the flat positioning of the contacts on the resistor
element the contacts form a natural spacer. An integrated circuit
positioned on the contact pins is protected by the contacts from
mechanical contacting with the resistor element. In the area of the
contacts the integrated circuit can be formed in such a way that
the side turned towards the contacts is free of solder points, so
that only the board of the integrated circuit rests on the contacts
and thus an electrical contacting with elements of the integrated
circuit is avoided.
The electrical contacts preferably have a clearance of 1 mm-50 mm,
preferably 5-10 mm. This allows good determination of the battery
current.
It is also possible for the resistor element to be formed from at
least two electrical connection pieces and one resistance piece.
The electrical connection pieces can for example be made from a
non-ferrous metal, for example copper or aluminium or an alloy
thereof. The positioning of connection pieces may make it easier to
make available an electrical interface with the power conductor of
the vehicle electrical system, since with the help of the
connection pieces a cable lug or another receptacle for the power
conductor can be fashioned.
According to an advantageous embodiment, the contacts can be
positioned either in the area of the resistance piece itself, on
the transitions between the resistance piece and the connection
pieces or on the connection pieces.
A beneficial production of the resistor element is guaranteed by
the resistor element being in the form of flat parts punched or cut
from bars. If the resistor elements are produced from bars, then
tempering (destressing) is unnecessary, because otherwise if the
material of the resistor elements were unwound from a coil,
tensions would result in the resistor element.
In the event of the material of the resistor element being
processed from a coil, according to an advantageous embodiment it
is proposed that the resistor element is formed by a flat part that
is initially unwound from a coil, then punched or cut and finally
tempered.
A further subject matter of the application is a method for
producing such a motor vehicle battery sensor element.
The method comprises the steps of positioning two spatially
separated electrical contacts on a resistor element. The electrical
contacts are also electrically connected to the resistor element.
Finally, the electrical contacts are coated with metal together
with the resistor element. The metal coating can for example be
tin.
In the following the subject matter of the application is explained
further using a drawing illustrating embodiments. The drawing shows
as follows:
FIG. 1a a view of a conventional resistor element.
FIG. 1b a cutaway view of a conventional resistor element.
FIG. 2 a cutaway view of a resistor element according to the
application.
FIG. 3 a top view of a resistor element according to the
application.
FIG. 4 a cutaway view of a resistor element with an integrated
circuit.
FIG. 5 an electrical equivalent circuit diagram of an arrangement
according to FIG. 4.
FIG. 6 a schematised shape of the resistances as a function of
temperature.
FIG. 1 shows a resistor element 2 with two connection pieces 4a, 4b
and a resistance piece 6. The connection pieces 4a, 4b can for
example be made from copper or alloys thereof. The resistance piece
6 can be made from a resistive material, for example Manganin,
Tungsten, Zeranin or similar. Between the connection pieces 4a, 4b
and the resistance piece 6 there is a material closure. The
resistance piece 6 is formed in such a way that with the surface of
the connection pieces 4a, 4b it creates a step. This can take
place, for example, by a resistance piece 6, having a smaller
thickness than the connection pieces 4a, 4b, being materially
connected with connection pieces 4a, 4b. The connection pieces 4a,
4b can have recesses 8 for power conductors. The connection pieces
4a, 4b can be formed in such a way that they form a battery clip
and allow a connection to a power conductor in a motor vehicle.
The step, formed by the resistance piece 6, in the surface 10 of
the resistor element 2 is used, as shown in FIG. 1b, in order to
guarantee sufficient clearance between an integrated circuit 12 and
the resistance piece 6. The integrated circuit 12, by means of
contacts, as shown in FIG. 1b, is electrically contacted with the
connection pieces 4a, 4b. The contacts 16 are spot positioned on
the surface 10 of the resistor element 2. Via the contacts 16 the
voltage dropping across the resistance piece 6 can be measured. The
contacts 16 also allow picking up of the temperature of the
connection pieces 4a, 4b, which along with other physical variables
is evaluated in the integrated circuit 12.
At the electrical contacts between the connection pieces 4a, 4b and
the resistance piece 6 a thermoelectric potential results, which
affects the voltage tapped via the contacts 16. Via the contacts
16, by means of the integrated circuit 12, the battery current
flowing along the connection piece 4a, the resistance piece 6 and
the connection piece 4b, is to be measured. This battery current
causes a drop in voltage across the resistance piece 6, which is
measured by the integrated circuit 12. By means of the
thermoelectric potential resulting at the contacts between
connection pieces 4a, 4b and resistance piece 6 apart from the
voltage actually caused by the battery current in resistance piece
6 a further voltage is measured. The thermoelectric potential is
temperature variant, however, so that at one and the same battery
current but at different temperatures differing voltages will be
measured in the integrated circuit 12. This leads to a distorted
measurement result. Since, as shown previously, the measurement of
the battery current plays a significant role in the operation of a
motor vehicle, inaccuracies in the measurement result caused by
thermoelectric potential can lead to malfunctions.
FIG. 2 shows a cutaway view of a resistor element 2, in which the
previously mentioned problems do not arise. FIG. 2 shows connection
pieces 4a, 4b, which are materially connected with the resistance
piece 6. It should be pointed out that the use of the connection
pieces 4 is purely for illustration purposes. A resistor element
can also be formed simply from the resistance piece 6 or the
resistance piece 6 and a connection piece 4. The electrical
contacts 16 are positioned on the resistance piece 6. In the
embodiment shown the connection pieces 4a, 4b are made from copper
and the contact elements 16 are likewise made from copper. The
resistance piece 6 is in the form of a shunt and for example can be
made from Manganin. Between copper and Manganin a thermoelectric
voltage results because of the differing K-values. This means that
as the temperature changes the contact voltage between the
connection pieces 4a, 4b and the resistance piece 6 or the
resistance piece 6 and the contact elements 16 changes. At constant
current through the resistance piece 6 via the contact elements 16
a changed voltage is measured as the temperature varies. In order
to balance this temperature variance, it is proposed that a metal
coating 8, which for example can be made from tin, is provided. The
metal coating 8 encloses the resistor element 2 and at the same
time the contact elements 16, with no seam. Through a suitable
coating 8, the thermoelectric voltage of the transition from
resistance piece 6 to the contact elements 16 or connection pieces
4 can essentially be short-circuited.
FIG. 3 shows a resistor element 2 according to an exemplary
embodiment. It can be seen that the contacts 16 are positioned on
the surface 10 of the resistor element 2, which according to the
exemplary embodiment shown is in the form of a single resistance
piece 6. Arrows 18 indicate the two possible directions of flow of
the current in the resistor element 2. The current flows through
the element 2 in the direction of the arrow 18a or in the direction
of the arrow 18b. It can be seen that the contacts 16 positioned
flat on the resistor element 2 are positioned orthogonally to the
direction of flow of the current on the surface 10 of the resistor
element 2. The contacts 16 are preferably applied using ultrasound
welding to the surface 10 of the resistor element 2. The contacts
16 are preferably in the form of wires, but can also be in the form
of shaped conductors with a rectangular or square cross-section. As
can be seen, the contacts 16 are preferably flush with the edges of
the resistor element 2. The contacts 16 are positioned on the
surface 10, which is the broad surface of the resistor element 2.
Along their direction of extension the contacts 16 are connected to
the surface 10 of the resistor element. Via the contacts 16 an
integrated circuit 12 can be connected to the resistor element
2.
A particularly good contacting of an integrated circuit 12 with the
resistor element 2 is for example then possible if the contacts 16,
as shown in FIG. 3, are bent at the edges of the resistor element 2
so that the ends of the contacts 16 protrude from the plane of the
surface 10 of the resistor element 2.
From FIG. 3 it can likewise be seen that the entire resistor
element along with the contacts 16 is coated with the coating 8.
The coating 8 ensures that temperature changes have little, if any,
effect on the battery current measurement result.
FIG. 4 shows a side view of a resistor element 2 with an integrated
circuit 12. The resistor element 2 is contacted via the contacts 16
with the integrated circuit 12. The contacts 16 are connected to
the integrated circuit 12 via solder points 22. The ends of the
contacts 16 are bent, so that contact pins result via which the
integrated circuit 12 is electrically connected to the resistor
element 2. Because the contact pins of the contacts 16 protrude
from the plane 10 of the resistor element 2, forces 24, acting on
the integrated circuit 12 or the resistor element 2, can be
balanced between resistor element 2 and integrated circuit 12. The
contact pins thus serve as spring elements, able to absorb forces.
As can be seen, the distance 26 between the integrated circuit 12
and the resistor element 2 is determined by the diameter of the
wires of the contacts 16. The wires of the contacts 16 thus serve
as spacers between resistor element 2 and integrated circuit
12.
The contacting of the integrated circuit 12 via the solder points
22 according to the advantageous embodiment does not have any
voltage equivalent of thermal energy. The solder points 22 are
preferably in the form of tin, as is the coating 8 on the surface
10 of the resistor element 2. The coating 8 is likewise provided on
the contacts 16, so that the solder points 22 are positioned on a
tinned surface. During measurement of the current through the
resistor element 2 a voltage is tapped between the contacts 16.
This voltage is the result of the current through the resistor
element 2 and the resistance between the contacts 16 of the
resistor element 2. Conventionally the resistance is in the range
50 to 500 .mu..OMEGA., preferably 110 .mu..OMEGA.. At the
transition between the resistance piece 2 and the contacts 16 a
thermoelectric potential results. In order to suppress this
thermoelectric potential, the coating 8 is provided. Through the
coating 8 the thermoelectric voltage between the contacts 16 and
the resistor element 2 is essentially short-circuited.
FIG. 5 shows an electrical equivalent circuit diagram of a circuit
arrangement according to FIG. 4. A measuring resistor R.sub.Mn is
shown, which is the resistance of the resistor element 2 between
the contacts 16. Further, a resistance R.sub.Sn is shown, which is
the resistance of the coating 8 between the solder points 22. In
series with the measuring resistance R.sub.Mess the thermoelectric
potential U.sub.MnCu are shown. The thermoelectric potential
U.sub.MnCu is temperature-dependent and is the result of the
different K-values of the resistor element 2 made from Manganin and
the contacts 16 made from copper as well as a possible temperature
difference. When measuring the voltage across the measuring
resistance R.sub.Mess with the help of the integrated circuit 12,
parasitic effects result through the thermoelectric potential
U.sub.MnCu.
Through the short-circuiting, shown by the broken line, of the
voltage U.sub.MnCu by the coating 8, these effects are minimised or
eliminated.
The resistances R.sub.Mn and R.sub.Sn are likewise
temperature-dependent. This dependency is determined by their
temperature coefficients .alpha.. In order to compensate this
temperature dependency as well, it is proposed that the coating 8
and the resistance piece are selected with corresponding
temperature coefficients such that the changes in resistances as a
result of temperature are compensated as far as possible.
FIG. 6 shows in a purely illustrative and schematic manner the
slope of temperature of the resistance R.sub.Mn and the slope of
temperature of the resistance R.sub.Sn. The representation is
merely to show how the temperature coefficients of the two
resistances are essentially selected such that the
temperature-dependent slopes of the two resistances R.sub.Mn and
R.sub.Sn are essentially opposed, so that for a parallel connection
of the resistances R.sub.Mn and R.sub.Sn essentially the overall
resistance remains the same.
Through the coating of the resistor element shown, measurement
errors as a result of temperature are essentially eliminated or
reduced so that the measurement accuracy of a motor vehicle battery
sensor element is increased.
* * * * *